The Two Different Effects of the Potential Neuroprotective Compound Minocycline on AMPA-Type Glutamate Receptors

Abstract

Background: Minocycline has demonstrated neuroprotective effects in experimental neurodegenerative diseases. The aim of this study was to investigate if there is any direct interaction between minocycline and the AMPA-type receptor channels, and to elucidate the underlying molecular pharmacological mechanisms. Methods: The patch-clamp technique was used combined with an ultrafast solution exchange system to investigate the interaction of minocycline with recombinant AMPA-type glutamate receptor channels (homomeric GluR2flipGQ or nondesensitizing GluR2L504Y). Results: Dose-dependent decreases in the relative peak current amplitude (rAmp) and the relative steady-state current (rC_des) were found in coapplication experiments with GluR2L504Y receptors, but not in preincubation experiments. Furthermore, coapplication of 1 or 3 mmol/l minocycline showed a decrease in the fast time constant of current decay, and reopening currents were observed. But in the test with GluR2flipGQ receptors, rAmp, relative area under the curve and rC_des increased with increasing concentrations of minocycline, and the steady-state time constant also increased when 3 µmol/l glutamate were used as agonist. Conclusion: Minocycline modulates AMPA-type receptor channels in a combination of a weaker open-channel block effect and a stronger potentiation effect, and the latter effect arises mainly from attenuating the extent of receptor desensitization.